The spread of a hybrid vehicle is accelerated. With an improvement in battery performance or motor control technology, the ratio of use of an EV mode in which the hybrid vehicle runs only with a motor without using an engine (the ratio of use time of the EV mode to that of an HY mode) is increased, However, it is not possible to obtain a large output only with the motor, and a situation in which the HV mode in which the motor and the engine are used in combination is used still exists.
Many users desire to drive the hybrid vehicle in the EV mode as much as possible. To cope with this, a technology for increasing the ratio of use of the EV running mode is proposed in, e.g., Patent Document 1 to Patent Document 3.
The increase in the ratio of use of the EV running mode corresponds to a decrease in the ratio of use of the engine. If the engine is not used, a driving force (driving torque) may be insufficient when an accelerator pedal is depressed. Patent Document 1 discloses a technology for preventing acceleration performance from being impaired in the EV mode. According to the technology of Patent Document 1, when a driving torque reaches an EV running available maximum torque in accordance with an increase in accelerator position, a controller of the hybrid vehicle keeps the EV running available maximum torque until the accelerator position further increases a predetermined amount dACC, and switches from the EV mode to the HV mode when the accelerator position increases beyond dACC. According to the technology of Patent Document 1, it is possible to keep the EV mode without suppressing the accelerator position to a low level, and acceleration in the EV mode is scarcely impaired.
Patent Document 2 discloses a technology for displaying the accelerator position at which the EV mode is switched to the HV mode. A user can adjust the accelerator position so as to keep the EV mode based on the display.
In addition, Patent Document 3 discloses a technology for increasing the use ratio of the EV mode by suppressing an engine drive for warming up the engine or a catalytic converter of exhaust gas.